The present invention is directed toward batch processes and, more particularly, toward a system for storing and presenting sensor and spectral data for batch processes.
A batch process is a process in which a limited quantity of ingredients are added and processed in a step-wise fashion. A recipe defines the equipment, procedures and formula used to run a batch process. An automated batch process is typically controlled by a process control system having controller subsystems for controlling the valves, pumps and other physical equipment required to perform the batch process. When a plurality of batch processes are being run to produce a plurality of different products, a software batch management application is typically provided to interface with the process control system. In such a case, the controller subsystems store and execute control logic for executing procedures within the batch process (such as delivering ingredients to a reactor), while the batch management application will allocate and de-allocate equipment, store recipes, schedule batch processes, generate reports, and store and archive batch data. The batch management application may also provide process variable setpoints to controller subsystems and may control the execution of batch procedures, such as stopping a current batch procedure, or starting a subsequent batch procedure.
During or after the run of a batch process, it is often desirable to analyze the product of the batch process to ascertain its composition. The composition of the product may be used to control the batch process, to improve the batch process and/or to comply with governmental regulations. The product of a batch process is typically analyzed using a spectrometer. A spectrometer is a device that is used to determine the chemical composition of a sample using electromagnetic radiation, e.g., light. In a spectrometer, electromagnetic radiation is interacted with a sample to produce a spectrum that is detected and then analyzed to determine the composition of the sample. An emission spectrometer excites molecules of a sample to higher energy states and then analyzes the radiation emitted when the molecules decay to their original energy state. An absorption spectrometer passes light through a sample and measures the absorption of light at various wavelengths. In a dispersive type of absorption spectrometer, the light is separated into its component wavelengths using a prism or a holographic grating and the absorption at each wavelength is individually measured. In an interference type of absorption spectrometer, modulated light having a range of different wavelengths is passed through a sample to obtain a combined measurement of the absorption at the different wavelengths. The combined measurement is then converted into a spectrum using Fourier transform computations. This interference type of absorption spectrometer typically utilizes infrared light and, thus, is known as a Fourier transform infrared (FTIR) spectrometer.
An FTIR spectrometer typically includes a Michelson interferometer or other similar type of interferometer that splits a broadband beam of infrared light into two parts. A Michelson interferometer has four arms. A first arm contains a source of infrared light (such as a quartz-halogen bulb), a second arm contains a stationary (fixed) mirror, a third arm contains a moving mirror and a fourth arm is open. At the intersection of the four arms is a beam splitter that is constructed to transmit half of the impinging radiation and reflect the other half of the impinging radiation. The transmitted light beam strikes the fixed mirror and the reflected light beam strikes the moving mirror. After reflecting off the respective mirrors, the two light beams recombine at the beam splitter. The combined light beam is then directed through a sample cell containing the sample to be analyzed, which modifies the interference pattern of the combined beam. The modified beam then impinges on a detector.
For each wavelength of light, the distance traveled by the light from the moving mirror changes so as to be in and out of phase with the light from the fixed mirror, which causes the intensity of the wavelength of the combined light beam to change in a sinusoidal manner due to the additive nature of waves. For each wavelength, a plot of light intensity versus optical path difference for one scan of the moving mirror is called an interferogram. A scan of the moving mirror is one complete movement of the mirror along its travel path.
Since the light used in the interferometer has a plurality of different wavelengths, the detector measures a total interferogram, which is the summation of all the interferograms from all the different infrared wavelengths. Thus, the total interferogram is a sum of sinusoidal waves, each of which contains information about the wavenumber of a given infrared peak and amplitude information about the peak intensity at that wavenumber. The Fourier transform computations transform the summed sinusoidal waves into a raw spectrum. This raw spectrum not only contains information about the sample, but about the spectrometer as well. To obtain information only about the sample, another calculation is performed using a reference or background spectrum. A background spectrum is taken before starting the analysis of the sample, when there is no sample in the cell (or there is a blank sample). The background spectrum only contains information about the spectrometer, including the sample cell, etc. The raw spectrum is ratioed against the background spectrum to produce a transmittance spectrum, which is then converted to an absorbance spectrum in the form of absorbance versus wavenumber. FIG. 1 shows an interferogram for a sample and FIG. 2 shows the absorbance spectrum of the sample. The interferogram, the raw spectrum and the absorbance spectrum from an FTIR spectrometer may be collectively referred to as “spectral data”.
The absorbance spectrum is used to determine the presence and concentration of a chemical species, or analyte, within a sample based on the wavenumber or range of wavenumbers absorbed and the magnitude of the absorbance of particular spectral regions. In other words, an analyte will absorb radiation in particular spectral regions creating a characteristic spectral profile according to the chemical structure of the analyte. A chemometric model determined for an analyte calculates the concentration of that analyte as a function of the magnitude of the absorbance in these spectral regions. The chemometric model is determined using multivariate mathematical correlation techniques to develop the model based on spectral measurements of a number of standards wherein the concentration of the analyte being modeled is known
Typically, the spectral data from a spectrometer in a batch process is only stored if required for regulatory audit purposes. If stored, the spectral data is conventionally stored separate from other information about the batch process, such as sensor data (temperature, pH, pressure, etc.) and batch management data (e.g., batch start, batch stop, batch abort, batch runtime, equipment used, etc.).
It would therefore be desirable, to provide a system for use with a batch process, wherein the system stores spectral data from a spectrometer in association with sensor data and batch management data. The present invention is directed to such a system.